Polyarylene sulfide resins (hereinafter sometimes abbreviated as “PAS resin”), the representative of which is a polyphenylene sulfide resin (hereinafter sometimes abbreviated as “PPS resin”) are excellent in heat resistance, chemical resistance and the like and widely utilized for applications such as electric/electronic parts, automotive parts, water heater parts, fibers and films.
A polyphenylene sulfide resin is conventionally produced by using solution polymerization in which p-dichlorobenzene, and sodium sulfide or sodium hydrosulfide, and sodium hydroxide are used as raw materials to polymerize in an organic polar solvent (e.g., see Patent Literature 1). Polyphenylene sulfide resins which are currently commercially available are generally produced by this method.
However, since dichlorobenzene was used for a monomer in the method, the concentration of halogen remaining in the resin after synthesis tends to be high. It was also necessary to perform polymerization reaction under a severe environment of high temperature and high pressure/strong alkaline, which requires to use a polymerization vessel using titanium, chromium or zirconium, which is expensive and hard-to-process, for the wetted part.
Accordingly, methods for producing a polyarylene sulfide resin without using dichlorobenzene as a monomer for polymerization and under moderate polymerization conditions are known. For Example, Patent Literature 2 discloses a solvent-soluble poly(arylene sulfonium salt) as a precursor for synthesis of a polyarylene sulfide resin. Poly(arylene sulfonium salt) is produced through a method of homopolymerizing a sulfoxide having one sulfinyl group (hereinafter, also referred to as “monofunctional sulfoxide”) such as methyl phenyl sulfoxide in the presence of an acid (e.g., see Patent Literature 2 and Non Patent Literature 1).